1. Field of the Invention
The present invention relates to a conductive resin composition used for an electrode material of a slider-type electronic component such as an encoder, specifically to a conductive resin composition capable of enhancing the wear-resistance between electrodes and sliding contacts to thereby extend the life of the contacts and an electrode substrate using the conductive resin composition, and a method of manufacturing the electrode substrate.
2. Description of the Related Art
In the slider-type electronic component such as an encoder or a variable resistor, the rotating part thereof rotates in a state that the sliding contacts and electrodes (conductive parts) maintain contact with each other, and thereby outputs pulse signals and varies the resistances.
As the sliding contact, a material capable of coming in contact with the electrode with a constant elasticity is preferred, for example, a high-elastic phosphor copper is generally used.
On the other hand, as the electrode side, an electrode is made by a method of applying nickel-plating to the surface of a copper plate, further applying silver-plating to the surface thereof, and thereafter punching it with a press mold, and forming it into a specified shape as the electrode. The electrode thus made is inserted into a metal mold, and is formed together with an insulating molten resin by the insert molding, and is fixed on a resin substrate, thus the electrode substrate is manufactured.
There is another method of forming an electrode by applying a conductive paint(ink) having a conductive resin composition dissolved with an organic solvent on an insulating substrate formed in advance into a specific shape. That is, the paint is made by mixing and dispersing graphite, carbon black, carbon fiber as a conductive filler, and glassy carbon as a wear-resistant reinforcing agent in a resin solution made by dissolving a heat-resisting resin such as phenolic resin, phenol-alkyl resin, or polyimide in an organic solvent; the paint thus made is applied on a substrate of Bakelite or alumina or the like by means of the screen-printing, and thus the electrode is formed.
Since this method facilitates to form the electrode with an arbitrary shape on a substrate, in the case that the production quantity is comparably small and the shape of electrode differs by production lot, the method easily reduces the cost of the electronic component in comparison to the case of manufacturing with the mold.
As mentioned above, the electrode substrate formed by the insert molding with the electrode having nickel-plating applied to the surface of a copper plate disposed in a resin material shows comparably low wear of the electrode by sliding with the sliding contact, because the strength of the electrode is good. However, the method of manufacturing the electrode substrate through the insert molding of the electrode involves complicated processes, and it requires the punching press molds each for the shapes of the electrodes, which swells the production cost. Also, the lead time for making the press molds becomes elongated, which makes it difficult to freely set the shapes of the electrodes.
On the other hand, in the method of forming an electrode on a substrate through the screen-printing, the surface hardness of the electrode thus formed is poor, and the electrode becomes easy to be worn when the sliding contact made of phosphor copper slides on the electrode with oppression. It is also possible to increase the hardness by adding a reinforcing agent such as glassy carbon or the like (more than 5 of the Mohs hardness). However, in the case of an electronic component such that the sliding contact slides on the surface of the electrode, the use of the glassy carbon or the like as the reinforcing agent makes the wear of the sliding contact noticeable, which makes it difficult to maintain the output waveform constant over a long period of time.